The present invention relates to a protecting device for clamps of a machine which works sheet shaped material.
In machines which work iron sheet or iron plate movements of the pieces being worked are produced by clamps gripping the iron sheets, these clamps being carried by movable carriages of the machine.
These clamps are provided, in most cases, with a protecting device intended to stop the machine if an obstacle is encountered. To this end, the machine comprises a stop device producing the instantaneous stopping of the machine. This device is arranged or connected between a protecting member, generally an iron wire, surrounding the clamping device, and a positive pole of a source of current, a negative pole of which is connected to earth or machine ground. It results from this arrangement that, if the clamps encounter a metallic element lying on their path, and which is connected to the mass of the machine, a feed circuit of the stop device producing the instantaneous stopping is closed, thus stopping the machine.
Such protecting devices exhibit the drawback that, if the obstacle is not conductive or if, the obstacle is conductive but is not in contact with the mass of the machine, the protecting device is ineffective. The fingers of the operator, for instance, are not protected by such a device.
The purpose of the present invention is to remove this drawback.